Microwave ovens have had electric heaters positioned inside the oven to aid in the cooking and/or browning process and have had electrically heated air or air used to cool electrical components such as magnetrons, power supplies, or magnetrons directed through the oven to aid in controlling vapors produced by a food body.
However, attempts to use the products of combustion in cooking regions excited with microwave energy have been generally unsatisfactory. Open gas flames in the oven can, among other things, act as sources of ionization which can absorb large portions of the microwave energy.